Summer is characterised by extreme drought and heat. Sealed surfaces and buildings hold the heat, making cities into heat islands. Rainwater, which could contribute to cooling cities, is diverted as wastewater, or it evaporates and seeps away without being used.
“It is urgently necessary to further secure urban water supplies, because demand for water in cities will increase significantly in the coming years,” explains Prof. Dr. Stephan Köster of the Institute of Sanitary Engineering and Waste Management (ISAH) at Leibniz University Hannover. Increased demand for water results, for example, from the watering of trees, parks and other city greenery; the replenishment of urban bodies of water; or the use of misting facilities in inner-city locations as an active form of heat protection.
The principle of a sponge city entails a completely new approach to water in the city, and one which is also in synergy with a city’s other climate-adaptation goals. In a sponge city, rainwater does not seep away unused or end up as wastewater. Instead, it is collected and saved – as it would be by a sponge. The water that is collected can be used to supply green areas and urban bodies of water, the so-called blue-green elements of a city – even during periods of drought. This can be supplemented by surfaces with a seepage function to keep the ground moist and increase the groundwater under cities. The sponge city approach also contributes to considerably mitigating the consequences of heavy rainfall. The capacity of the blue-green infrastructure on the city’s surface to retain water is significantly increased, which reduces pressure on the sewage system.
Prof. Dr.-Ing. Stephan Köster and Dr.-Ing. Maike Beier (ISAH) have developed an innovative concept for the management of rainwater in a sponge city using intelligent management of water levels and demand. The concept envisions the implementation of a complementary supply – alongside the drinking water supply – of so-called “city water” generated by the sponge city. Non-polluted or lightly polluted rainwater would be saved in the city’s sponge, while polluted rainwater would be diverted using the existing drainage infrastructure and treated at a wastewater plant. The water that is collected – and made safe via simple, decentralised treatment in so-called city water hubs – can be supplied in various levels of quality as city water and used in those settings where drinking water is not required or should not be used. The treatment process should utilise low-energy technologies and renewable energies.
The ISAH team’s approach thus goes much further than existing sponge city concepts, as the city water concept introduces a new, quality-oriented approach to rainwater management and a complementary, decentralised water-supply component. This reduces demand on a city’s water resources at the same time as the drinking water supply is increased. Simultaneously, the quality of urban wastewater disposal and flood prevention are improved.
Note to editors:
For further information, please contact Prof. Dr.-Ing. Stephan Köster and Dr.-Ing Maike Beier, Leibniz University Hannover Institute of Sanitary Engineering and Waste Management (tel: +49 511 762 3379; email koester@isah.uni-hannover.de).
